If it ever rained in Houston after June first and before Oct first each year I might find it easier to get interested in rain water harvesting. I’m also pretty sure the HOA would pitch a tizzy fit. But be that as it may I ran across this really cool idea on Rainwater Harvesting Vertically ( photo credit to Az Sustainably as well ) that might not freak out your HOA.
This design is a terrace that collects the rain water from your downspout and delivers it to your garden. I really like the design. I expect you could design it to go in front of your downspout and hide the downspout all together.
More information:
Rainwater Harvesting Texas AgriLife
Herself's Plants 
I like it! This weekend we saw a rain water collection system that used chains instead of downspouts way cool!
I’ve seen some decorative ones like that in S&H.
How’d they work?